This invention relates to a pressure differential automatic transfer type three-way valve utilized in a heat pump type refrigeration system.
As shown in FIG. 1, in a prior art heat pump type refrigeration system, an electromagnetically transferred three-way valve 2 (hereinafter merely called transfer valve 2) is provided on the discharge side of a compressor 1, and a pressure differential automatic transfer type three-way valve 3 (hereinafter merely called pressure differential valve 3) is provided on the suction or low pressure side of the compressor 1.
Between the transfer valve 2 and the pressure differential valve 3 are connected an indoor heat exchanger 4 and an outdoor heat exchanger 5 which are interconnected by a pressure reducing device 6 in the form of a capillary tube 6, etc. As is well known, the operation of the heat exchangers is transferred between a condenser and an evaporator depending upon whether the refrigeration system is operated as a heater or a cooler. The first port 2a of the transfer valve 2 is connected with the discharge side of the compressor 1, the second port 2b is connected with the second port 3b of the pressure differential valve 3 through a pipe l.sub.1, and the third port 2c of the transfer valve 2 and the third port 3c of the pressure differential valve 3 are interconnected through a pipe l.sub.2. The first port 3a of the pressure differential valve 3 is connected with the suction side of the compressor 1. Both heat exchangers 4 and 5 and the pressure reducing device 6 are connected in series across junctions P.sub.1 and P.sub.2 of the pipes l.sub.1 and l.sub.2.
As shown in FIG. 2, the differential pressure valve 3 comprises a cylindrical casing 7 and a slider 8 contained therein. The second port 3b and the third port 3c are formed on both sides of the casing 7, while the first port 3a is formed at a central portion thereof. Valve seats 9 are formed on the inner surface of the casing 1 near the center thereof. The slider 8 includes a pair of valve members 11 mounted on both ends of a shaft 10 to be slidable in respective large diameter portions 7a on both sides of the casing 7. When inclined or conical surfaces 11a of the valve members 11 engage the valve seats 9 at both ends of a small diameter portion 7b formed at the central portion of the inner surface of the casing 7, either one of the second port 3b and the third port 3c is closed. Thus, as the slider 8 is moved to the left or right, the flow of refrigerant is transferred.
In the refrigeration system described above, during the heating operation, the second port 2b of the transfer valve 2 is opened, its third port 2c is closed, while the pressure differential valve 3 assumes a state shown in FIG. 2 in which the slider 8 is moved toward right, thus closing the second port 3b and opening the third port 3c. Consequently, the refrigerant flows through a closed circuit including compressor 1, second port 2b of the transfer valve 2, indoor heat exchanger 4, pressure reducing device 6, outdoor heat exchanger 5, third port 3c of pressure differential valve 3 as shown by solid line arrows in FIG. 1.
At this time, the pressure Pd at the first port 2a of the transfer valve 2 and the pressure Pe at the junction P.sub.1 are high, whereas the pressure Pc at the junction P.sub.2 and the pressure Ps at the first port 3a of the pressure differential valve 3 are low.
To transfer the operation from the heating operation to the cooling operation, the transfer valve 2 is operated to open the third port 2c and to close the second port 2b. Then, at the instant of transfer, the refrigerant flows as shown by solid line arrows shown in FIG. 3. More particularly, the refrigerant flows from the third port 2c of the transfer valve 2 through pipe l.sub.2, the third port 3c and the first port 3a of the pressure differential valve 3. However, leakage is inevitable for the transfer valve 2 so that the leaked refrigerant flows through a shunt circuit between the second port 2b and the junction P.sub.1 through both heat exchangers 4 and 5 and the pressure reducing device 6 as shown by dotted line arrows in FIG. 3.
Under this state, pressure Pe is applied to the second port 3b of the pressure differential valve 3, while pressure Pc is applied to the third port Pc thereof with the result that a differential pressure Pe-Ps is applied to the slider 8 on its side of the second port 3b, while a differential pressure Pc-Ps to the slider on its side of the third port 3c.
Since the leaked refrigerant flows in the direction of dotted line arrows, the pressure Pe becomes higher than pressure Pc to establish a relation Pe-Ps&gt;Pc-Ps which the result that the slider 8 is still maintained in the state shown in FIG. 2 so that operation cannot be transferred to the cooling operation.
It has also been proposed to install a pressure differential valve 20 on the discharge or output side of the compressor 1 and to install a transfer valve 21 on the suction side of the compressor 1, as shown in FIG. 4. As shown in FIG. 5, the pressure differential valve 20 utilized in this system comprises a cylindrical casing 22 and a slider 23 contained therein. A first port 20a is formed at the center of the casing 22 and the second and third ports 20b and 20c are formed on the opposite ends of the casing. These two ports are ON-OFF controlled by inclined or conical surfaces 25a of valve members 25 on both ends of the shaft of slider 23, thus switching the flow of the refrigerant.
In this refrigeration system, during the heating operation shown in FIG. 4, the third port 21c of the transfer valve 21 is opened and second port 21b thereof is closed so as to move the slider 23 of the pressure differential valve 20 to the right to open the second port 20b and close the third port 20c. Under this state, the refrigerant flows in the direction of solid line arrows shown in FIG. 4 in the same manner as in FIG. 1.
To switch the operation from the heating operation to the cooling operation, the transfer valve 21 is reversed. Then, the refrigerant flows in the direction of solid line arrows shown in FIG. 6 but due to leakage of the third port 21c of the transfer valve 21 the leaked refrigerant flows in the direction of dotted line arrows shown in FIG. 6 (from junction P.sub.1 to junction P.sub.2), thus establishing a relation Pe&gt;Pc. At this time, since a dynamic pressure (Pd-Pe) is applied upon the second port 20b, whereas a dynamic pressure Pd-Pc is applied upon the third port 20c so that a relation Pd-Pe&lt;Pd-Pc is established with the result that the slider 23 would be still maintained at the righthand position shown in FIG. 5, thus preventing transfer of the pressure differential valve.
The transfer valves 2 and 21 can be substituted by two electromagnetic two-way valves, but in such modification too, so long as the prior art pressure differential valve is used it is impossible to transfer the operation.